In general, an image reading apparatus such as a scanner reads a document, temporarily stores the image data of the document in a storage, and then transmits the image data to an information processing apparatus such as a personal computer. When it takes a long time to transmit the image data to the information processing apparatus and the size of the image data that is not transmitted yet exceeds the storage capacity, the image reading apparatus interrupts the process of reading the document. The image reading apparatus is able to suppress interruption of the document-reading process, by reducing the amount of communication between the image reading apparatus and the information processing apparatus through compression of the image data, for example. However, the data amount after compression of the image data varies according to the amount of the image data and the like before compression. For this reason, data amount after compression is not always appropriate.
The following compression-ratio determination device has been disclosed (refer to Japanese Laid-open Patent Publication No. 2011-188068). Specifically, the compression-ratio determination device determines a compression ratio based on the amount of image data obtained by reading a document and communication capacity information so that the amount of data transmitted per predetermined time period would be larger than the amount of data read per predetermined time period.
In addition the above, the following image reading apparatus has been disclosed (refer to Japanese Laid-open Patent Publication No. 2005-86543). Specifically, the image reading apparatus estimates the compression ratio that is to be used for actually reading a document, based on the compression ratio of a preview image generated by reading the document at a low resolution, and then selects the optimal speed for reading the document, based on the estimated compression ratio and the effective transfer rate of the interface circuit.
The amount of image data after compression varies according to the document, and therefore is not necessarily optimal.